1. Field of the Invention
The present invention relates to a drive device for coupling a motor to a member.
2. Description of the Prior Art
It is known to provide a drive device for a control member which is drivable by way of a free wheel clutch comprising a wrap spring.
Such drive devices are, for example, used in heating, ventilation and airconditioning installations for actuating control members such as valves or flaps and the like. The drive devices operate over a certain rotary angle range which is defined by a mechanical stop at both ends to block rotation. The blocking effect stops the rotary movement of a motor but involves the disadvantage that, particularly in the blocked condition, the drive device generates unacceptably loud noises, the cause of which is the unsteady and erratic operation of the blocked or loaded motor.
The disadvantageous noise generation can be compensated for by means of load-dependent electronic limit off switches for the motor or through the insertion of a magnetic hysteresis coupling between the motor and the transmission.
It is known for a coiled-spring or wrap-spring clutch to be used in a drive device in order to decouple a drive motor from a maximum transmitted torque, in dependence on a subsequent transmission stage. Embodiments of wrap-spring clutches are known for example from EP 678 685 A1, U.S. Pat. No. 3,125,889 and U.S. Pat. No. 3,893,554.
A drive device of this kind is known (DE 195 16 973 A1) in which a control wheel of a control member is coupled to a drive motor by way of a freewheel clutch, the freewheel clutch being embodied in the form of a wrap-spring clutch.
When wrap-spring clutches of that kind are used however the described noises are generated in the respective transitional ranges in which the wrap-spring clutch becomes operative.